Such an extrusion press is known from DE 20 03 244 A (GB 1,287,892). The holder together with the billet gripper or receptacle is supported in a yoke so as to be pivotable about a vertical axis. However, it is still possible for the billet gripper to become misaligned with the die and the pressing stamp, so that extrusion of the billet is hindered or even impossible. To allow adjustments to be made to the central axis, the entire holder carriage can be adjusted and set in the vertical direction by means of screws, and in the transverse, i.e. lateral, direction by adjusting the slide webs for the holder carriage.
In one extrusion press known from DE 195 00 555 C1 (U.S. Pat. No. 5,855,135), the charging into the billet gripper (not described) of a billet to be pressed is usually performed by transferring a billet, preheated in a furnace to the pressing temperature, into loading trays and, using swivel arms mounted to a shaft in a rotationally fixed manner—referred to as swivel loaders, as an alternative to linear billet loaders that are also commonly used—swiveling it in the press axis into the unoccupied space between the die and the press plate. By use of adjusting cylinders a running beam and the holder carriage that is movable on the guides of the press frame may be displaced on the die or the counter beam, the billet gripper being inverted above the billet. Corresponding to the advancement of the holder carriage together with the billet gripper, the axially movable swivel arm is moved on the shaft until the billet is clamped between the pressing stamp or mandrel and the counter beam or die fastened in a holder. The holder carriage is moved by means of lateral cylinders.
During the extrusion pressing, high compression stresses are present in the billet that allow a high degree of deformation. A prerequisite for this high degree of deformation is a low yield stress of the material being shaped. For this reason pressing is performed only at high temperatures. For aluminum materials the pressing temperature is 400 to 500° C., for copper materials, 600 to 900° C., and for stainless steel or special materials, up to 1250° C. The thermal expansion unavoidably associated with these high temperatures makes it very difficult to maintain the central position of the billet gripper with respect to the press axis.
From previously cited DE 195 00 555 C1 it is known to support the holder and running beam on support surfaces that are angled in such a way that their extension intersects the press axis or is close thereto, thus being oriented to the press axis, in order to prevent the central position of the receiver and the pressing stamp from being influenced by thermal expansion caused by changes in temperature. For central alignment of the receiver and the pressing stamp on the press axis, for the base frames that support the guides for the holder carriage together with the holder and the running beam, supports are provided between the guides and base frame that are horizontally adjustable on the base frame transverse to the press axis, and with respect to which the guides are vertically adjustable.